With forests in peril, she’s on a mission to save ‘mother trees’
Suzanne Simard, who made key discoveries on how fungal networks sustain healthy forests, is now pushing to reform logging
MALCOLM KNAPP RESEARCH FOREST, British Columbia — Suzanne Simard walks into the forest with a churchgoer’s reverence. The soaring canopies of Douglas firs are her cathedral’s ceiling. Shifting branches of cedars, maples and hemlocks filter the sunlight like stained-glass windows. A songbird chorus echoes from the treetops, accompanied by the wind whistling through pine boughs and a woodpecker’s steady drumming.
But beauty alone is not what makes this place sacred to Simard. In each colossal tree, the University of British Columbia forest ecologist sees a source of oxygen, a filter for water and a home for hundreds of different creatures. To her, the lush, multilayered understory is proof of a thriving community, where a variety of species ensures that every wavelength of light is put to good use.
And although Simard cannot hear their conversation, she knows the trees are in communion with the fungi beneath her feet — bartering carbon for water and nutrients in a raucous exchange older than the forests themselves.
Crouching low, Simard pulls a trowel from her pocket and cuts deep into the earth, through layers of moss, duff and debris.
“See this?” In her cupped hands, she holds a palmful of soil flecked with thin, white filaments. “Mycorrhizal fungi,” she says. “It’s joining all these trees together.”
Through decades of study, Simard and other ecologists have revealed how fungi and trees are linked in vast, subterranean networks through which organisms send messages and swap resources. The findings have helped revolutionize the way the world sees forests, turning static stands of trees into complex societies of interdependent species, where scenes of both fierce competition and startling cooperation play out on a grand scale.
Now, Simard is attempting to translate that research into a road map for protecting forests from the demands of logging and the ravages of climate change. In an experiment spanning hundreds of miles, she and her colleagues aim to show the benefits of preserving “mother trees” — giant elders of the forest, which Simard believes play a critical role in maintaining fungal networks, nurturing younger seedlings and safeguarding millions of tons of carbon stored in vegetation and soil.
Adopting such practices would fundamentally alter forest industries, Simard admits. It would mean logging less, using fewer wood-based products and investing more in restoring battered ecosystems. It would require people to behave a bit more like creatures of the forest — to recognize our interdependence, to learn from elders, to take less than we give.
But she argues that change is necessary to avert dangerous warming that threatens both trees and humans.
“What it comes down to,” she says, “is we have to save our forests, or we’re done.”
Opening her cupped palms, Simard allows her handful of fungal filaments to fall back to the earth.
“It comes down to whether we value our environment as something to take from, or something to tend.”
The hubs of the forest
Simard brushes dirt from her hands, then trudges to the edge of the stand. “Let’s go see the clear cut.”
On the other side of the road is a 50-acre expanse of tree stumps, shrubs and child-sized Douglas fir saplings. A sign identifies it as part of Simard’s Mother Tree Project, one of five experimental plots here in the Malcolm Knapp Research Forest, an hour east of Vancouver, Canada.
With her trowel, Simard digs another hole in the ground. Four years after the plot was logged and replanted, the soil is dusty and shallow. There’s little of the moss and partly-decomposed debris she found in the uncut forest.
“There’s hardly any forest floor left,” she says.
Simard’s career began in landscapes like this one. The daughter and granddaughter of tree cutters, her first job was as a forester for a Canadian logging company, flagging the biggest and most valuable trees to be harvested and hauled away. Afterward, the clear-cut site would be sprayed with herbicides — a measure meant to help newly planted commercial seedlings by killing off competitors for sunshine and nutrients.
But Simard noticed the replanted landscapes didn’t appear as healthy as the forests they had replaced.
“It just felt wrong,” she says. “I saw the forest as a connected place … and we were ripping it apart.”
So she sought out evidence to support her instincts. For her doctoral thesis at Oregon State University, Simard used radioactive carbon as a chemical tracer to show sugars moving between trees of different species connected by the fungal network. When one tree was moved into the shade, making it harder to perform photosynthesis, it received extra carbon from the other plant.
The 1997 findings were splashed across the cover of Nature, one of the most prestigious scientific journals, under the headline “The Wood-Wide Web.” Simard became something of a scientific celebrity — she headlined TED Talks, starred in documentaries and inspired a character in the Pulitzer Prize-winning novel “The Overstory.”
Yet Simard’s studies were just one part of a flourishing new field of research on fungal networks. Scientists now know that over 90 percent of all terrestrial plants form mycorrhizal partnerships — the legacy of a half-billion-year-old alliance that likely helped plants migrate from the oceans onto land.
The fungi provide a foundation for underground food webs. Their lacy architecture retain filter water and prevent erosion by giving structure to the soil.
And, crucially, these networks serve as a link in the biological chain that shuttles carbon from the air, into trees, through fungi and then deep into the ground. Studies suggest that as much as 20 percent of the carbon taken up by plants is transferred to their fungal symbionts, allowing the world’s mycorrhizal fungi to sequester at least 5 billion tons of carbon dioxide each year.
“It’s dizzying to think about all of those interactions that are happening under our feet,” said Toby Kiers, an evolutionary biologist at Vrije Universiteit Amsterdam.
As the importance of mycorrhizal networks became more and more clear, Simard wanted to map the unseen systems. In an experiment led by graduate student Kevin Bieler, Simard’s team painstakingly tested the DNA of every tree and fungus in a 10,000-square-foot patch of forest. They discovered genetically identical fungi on the roots of as many as 19 different trees — often linking young saplings to forest veterans. The largest, oldest trees boasted by far the most fungal connections.
In scientific papers, Simard refers to these highly-connected individuals as “hub trees” or “legacy trees.” But in her heart, and in interviews, they are “mother trees” — grand, nurturing and wise.
Simard’s studies have showed that emerging plants fare better when mycorrhizal fungi connect them to mother trees. The ancient giants appear to recognize their kin, allocating more resources to sibling seedlings than to unrelated organisms.
They might even behave altruistically; in one lab experiment, Simard witnessed trees under life-threatening attack from insects sending a flood of carbon into the fungal network.
“I’m not saying it’s always harmonious,” Simard cautions. As in any community, forest relationships can be fraught. Tree still compete for light and nutrients. Their fungal symbionts sometimes take more sugar than the host can afford to give.
“But out of diversity and connection,” she says, “a beautiful and productive forest emerges.”
Other scientists are less sure about the importance of these ties.
“In my mind, it’s still an open question,” says Stanford University mycologist Kabir Peay. He pointed out that most research on carbon transfers between trees has taken place in labs, which are poor replicas of a forest’s true complexity.
[Ruby, the Capitol Christmas Tree, is part of a species in climate peril]
Even some of Simard’s experiments offer “equivocal” evidence for the role of mycorrhizal networks, Peay adds. One 2009 study found that the fungi appeared to boost the growth of trees that emerged directly from seed, but had no effect on planted seedlings.
Kiers also worries that Simard’s “anthropomorphic” framing erases scientific nuances — and in doing so, misses some of nature’s mystery.
Yet both scientists agree on the urgency of protecting fungal networks.
“It’s unclear whether we know enough about these communities to improve the outcomes we want in the face of a changing climate,” Peay says. “But I think we need to try.”
‘We’re ripping up our carbon sinks’
Despite the revolution in scientists’ understanding of this terrain, Simard says forestry hasn’t changed much since her early days in the woods.
Researchers estimate that more than 90 percent of British Columbia’s towering ancient forests have been cut down, and another 94,000 acres of old growth is lost each year. The vast majority of this logging involves clear-cuts or “clear-cuts with reserves,” where just a tiny patch of trees is left standing, leaving mycorrhizal fungi to wither without their plant partners. And since the biggest, oldest trees provide the most valuable timber, companies often target them first.
Meanwhile, provincial regulations still mandate that replanted areas be “free to grow” without competition — nudging forest managers to cultivate same-aged “plantations” of just a few species, rather than fostering more diverse landscapes.
[This tree has stood here for 500 years. Should it be sold for $17,500?]
This approach may jeopardize the networks forests need to survive. Simard has found that tree plantations harbor just a tenth of the fungi species found in mature wild forests. Separately, a team of Swedish researchers showed that logging in Scots pine forests shrank the fungal community by 95 percent.
And when trees are removed from a landscape, it unleashes the carbon buried below, studies by Simard and others show. A 2019 report by the Sierra Club found that logged and replanted forests in British Columbia remain net carbon emitters for at least 13 years after being harvested. The province’s own data show that forest management generates more than 40 million tons of carbon dioxide each year — equal to the annual emissions from 101 gas-fired power plants.
“It’s just so crazy,” Simard says. “We’re ripping up our carbon sinks and using petrol to ship it all over the world. … We’re just making the problem worse with all these policies and these decisions.”
Here at Malcolm Knapp, the toll of warming is already plain. By this point in late October, autumn rains should have turned the soil into soggy, springy mush. Instead, desiccated twigs crunch like potato chips each time Simard takes a step. The day is unseasonably hot, and the air carries the scent of wood smoke from more than two dozen wildfires burning in the region.
Degraded, disconnected and deprived of their fungal partners, Simard worries about how replanted forests will endure in a changed climate. Human greenhouse gas emissions have already warmed the Earth by more than 1.1 degrees Celsius (2 degrees Fahrenheit). Droughts are longer, wildfires more ferocious and insect plagues are surging.
Will missing mycorrhizal fungi make plantation trees more vulnerable to marauding pests, she wonders? Will seedlings succumb to water scarcity without mother trees helping them grow?
“Maybe in the past, some of those plantations would do okay,” Simard says. “But with these additional stresses on forests — I don’t know what it’s going to be like. But I’m afraid for them.”
Saving the mother trees
Now it’s up to us to protect forests from the problems we’ve created, Simard says. That’s the goal of the Mother Tree Project: to understand what forests need in a changing climate, so people can play a helpful role in the communities that plants and animals and fungi have fostered for thousands of years.
The experiment encompasses nine forest sites scattered across more than 600 miles of British Columbia, each with slightly different environmental circumstances. The coastal sites are warm and wet; the interior ones are drier. There’s harsh cold at northern latitudes and rising heat to the south. This creates a “climatic gradient,” Simard says, allowing her to test how forests function in varying conditions and predict what might happen as temperatures rise and precipitation dwindles.
At every site, Simard partnered with logging companies to conduct five “treatments,” or harvesting methods. One experimental plot was left untouched, to act as the control. A second was clear cut, representing the status quo.
[Gene editing could revive a nearly lost tree. Not everyone is on board.]
At another plot, the crew removed 90 percent of the forest, until only the mother trees remained. For yet another, they left the mother trees amid clusters of neighbors, creating islands of green amid a shorn landscape. And in the final, least intensive treatment, they kept 60 percent of the forest standing, so there were no significant breaks in the canopy.
The plots were logged four years ago and replanted with a mix of Douglas fir, larch and pines. Now Simard and her team must watch to see what happens. They visit each plot every year or so, taking several days to document each tree, shrub, moss and mushroom. Planted seedlings get a checkup. Fungi are collected for DNA tests. Leaves, debris and soil are packed away into dozens of brown paper bags; when they get back to the lab, technicians dehydrate the material and calculate how much carbon it contains.
Despite her misgivings about some of Simard’s language, Kiers calls the setup “a beautifully designed experiment.”
“What happens to the fungal community under these treatments … is one of the ideas we really would like to understand,” she says.
The full results of the Mother Tree experiment won’t be known until the replanted forests reach maturity, decades from now. But some takeaways are already clear, Simard says.
Given the immense amount of carbon stored in ancient, uncut forests, she believes governments should cease all logging there.
“It just doesn’t make sense,” she says. “Any trees that are planted are going to take hundreds, if not thousands, of years to recover those carbon pools. And that’s outside the time frame we have to change things.”
In “secondary forests” — ecosystems that have regrown after being logged a century ago — Simard says logging should look like the least intensive treatment in the mother tree experiment. At these sites, her team has found, leaving more than half the forest intact helped create “refuges” for mycorrhizal fungi and increased regeneration of new trees.
[These trees have survived more than 1,000 years. Can they survive climate change?]
In a 2020 study in the journal Frontiers in Forests and Global Change, Simard and her colleagues also reported that ecosystems held onto much more carbon when their canopy was kept intact. The benefit was especially apparent at the Mother Tree Project’s drier research sites. There, clear-cut plots lost more than 60 percent of their total ecosystem carbon, compared to an 8 percent decline in plots where more than half the trees remained.
As climate change dries out Western forests, the researchers wrote, these techniques will become even more vital to keep carbon out of the atmosphere.
Malcom Knapp manager Hélène Marcoux, who oversees both research and logging in the forest, cautions that this kind of harvest would come with trade-offs. Selective logging by hand can be more dangerous than clear-cutting with machines. It’s also more expensive, which would increase the cost of building materials and other products made from wood.
“But there are also so many things to gain,” Marcoux says. “We won’t get all that money now, but we will guarantee something for the future.”
Nor is this approach anything new. It’s how First Nations people have cared for this landscape for hundreds upon hundreds of years, Simard says. “We need to be listening to the land like they did, like they still do.”
Here in Simard’s healthiest experimental plot, the one where 60 percent of the tree cover was allowed to remain, the forest offers reminders of its resilience: Deep soil. A wealth of mosses. Honey-colored light that drips through the layered branches of trees.
Despite traces of the harvest that occurred four years ago, this place still feels sacred and irrepressibly alive.
Then Simard spots a spindly Douglas fir tree, barely a foot high. She pauses, thinking it was one of the seedlings her crew planted after the harvest. Yet its stem is faintly curved — a sign of a tree that has sprouted on its own.
Once more, Simard retrieves her trowel and gently works the tree free of the soil, exposing an expansive tangle of roots entwined with barely discernible threads of fungi. “It’s a natural,” she confirms. Unlike pampered, nursery-grown trees, the fir had to develop an “exploratory” root system to get the nutrients it needed.
Now, whatever threats loom ahead of the forest — drought, invasive plants, nutrient shortages — the tree’s ample roots and mycorrhizal partners will help it access what it needs to survive.
But Simard still wants to give it a boost. Gently, she nestles the sapling back into the earth, then empties her water bottle into the parched ground.
“Good luck,” she says. “Good luck little tree.”